The present invention relates to a method for cold gas spraying, in which, to coat at least one substrate or to produce at least one molding, particles are accelerated to the surface of the substrate or molding in the unmelted state by means of at least one gas jet and adhere there under the conversion of their kinetic energy (cf. published document EP 1 382 720 A2 from the prior art).
The present invention furthermore relates to a device for coating at least one substrate or for producing at least one molding by means of at least one cold gas spraying pistol, wherein the cold gas spraying pistol and the substrate or molding to be coated are arranged in a vacuum chamber (cf. EP 1 382 720 A2 from the prior art).
Conductors and coils, particularly superconducting coils, are conventionally principally produced as wires, often in the form of a copper matrix with filaments of the superconductor. Mention may be made here, for example, of niobium-titanium (NbTi) or also of niobium-tantalum as an important superconducting material. Especially in the case of brittle materials, particularly in the case of high-temperature superconductor materials (what are known as HTSC materials), production takes place in complex sintering processes.
The wires produced in this manner are subsequently wound to form coils, for the most part on coil formers that are used for the stabilization of the coil. Additionally, the wires can also be cast in, for the most part in synthetic resins. This casting in synthetic resins serves to stabilize the coils completely, so that the coils can withstand the large forces acting in the superconductively-generated magnetic field. Large forces of this type act in particular in devices for nuclear magnetic resonance (NMR) imaging and in devices for nuclear magnetic resonance (NMR) spectroscopy.
If individual coil portions are not sufficiently fixed, then the micro-movements occurring lead to the breakdown of the superconduction (what is known as quench, in which the superconductor changes suddenly from the superconducting state to the normal-conducting state, whereby a great deal of heat is generated; quench is particularly dangerous in the case of superconducting coils, as the entire field energy is converted to heat there when the superconduction breaks down).
In the published document DE 38 06 177 A1 from the prior art, the use of ceramic powder with superconducting properties as a starting material for the application of high-temperature superconductor material to workpieces by means of thermal spraying is disclosed. The superconducting properties are regenerated by means of a targeted heat treatment following the spraying on.
According to this published document DE 38 06 177 A1, the current carrying capacity of the high-temperature superconductor layers is improved in that the thermal spraying takes place under conditions in which the particles in the spray jet have a low characteristic temperature and a high airspeed, as a result of which, when impinging onto the substrate, a high degree of deformation is effected. The subsequent heat treatment takes place in such a manner that a growth in the grains of the crystallites in the layer is achieved as a function of the degree of deformation.
In the published document WO 2006/061384 A1 from the prior art, a method for cold gas spraying is described, in which a gas jet is generated by means of a cold gas spraying pistol, into which gas jet particles are introduced. The kinetic energy of the particles leads to the formation of a layer on a substrate that has a structured texture that is transferred to the forming layer.
According to this published document WO 2006/061384 A1, a high-temperature superconducting layer can be created on the substrate by means of a suitable composition of the particles. This process can additionally be supported by a heating apparatus in a following heat treatment step.
With respect to the technological background of the present invention, attention may additionally be drawn to the publication “Microstructural characteristics of cold-sprayed nanostructured WC-Co coatings” by R. S. Lima, J. Karthikeyan, C. M. Kay, J. Lindemann and C. C. Berndt, Preparation and Characterization, ELSEVIER Sequoia, N L, Thin Solid Films 2002, Volume 416, Nos. 1-2, pages 129 to 135, as well as to the published documents U.S. Pat. No. 5,646,094, US 2002/0056473 A1, US 2004/0026030 A1 and WO 2004/044672 A2 from the prior art.